Matrix solar dish

ABSTRACT

A matrix solar dish concentrator with flexed glass mirrors is patterned from orthogonal planes parallel to the axis of symmetry of a paraboloid and intersecting the paraboloid, this pattern making all parabolic trusses uniform. Parabolic trusses are made by flexing linear truss members with lateral forces creating accurate parabolic member curves, restraining the flexed members with rigid webbing to form an orthogonal paraboloid frame. Parabolic glass mirrors are made by flexing slender flat glass mirrors with lateral forces creating accurate parabolic mirror curves, restraining the flexed mirrors with tension buttons connected to the orthogonal paraboloid frame to form a solar dish. Glass mirror structural substrates are not used. The solar dish tracks the solar azimuth with a bicycle wheel and tracks the solar zenith with a television satellite dish actuator. A solar receiver is supported with a low shade structure outside a cone of concentrated sunlight. Uniform flux is greater than 1000 suns and suitable for high-intensity photovoltaic cells and district heating systems.

CROSS REFERENCE

[0001] This application is entitled to the benefit of Provisional PatentApplication Ser. # 60/202,042 filed May 5, 2000.

FIELD OF INVENTION

[0002] This invention relates to solar concentrators, specificallyparaboloid dish reflectors used for concentrating solar energy ontonearby receivers.

BACKGROUND OF THE INVENTION

[0003] The Greenhouse Effect is a problem that can only be solved withcost effective solar energy systems. Solar collectors in remote areas inthe countryside can collect summer solar energy and supply city winterbase and peak heat and hot water demands by utilizing district heatdistribution with seasonal heat storage. Communities in Northern Europeare 100% solar heated with hot water in the winter using districtheating systems powered by solar collectors that operate only in thesummer.

[0004] Reflecting solar concentrators are the most efficient solar heatcollectors. The cost of materials compared with the energy deliveredindicates that solar concentrator technology should be exceedingly costeffective. There are thousands of solar concentrator designs and scoresof prototypes. However, the manufacture of solar concentrators does notexist. Complexity of implementation is a prior-art problem. Lack ofinformation, materials, and manufacturing skills create impediments formarket introduction and rapid expansion of cost effective solarconcentrators.

[0005] Prior-art mirrors used in solar concentrators are commonly madefrom flat glass coated with silver, followed by moisture protectionlayers made from copper films, paint, sheet metal, or a second layer offlat glass or glass like substance. Silvered low-iron glass mirrors are96% efficient. Painted glass mirrors have long-term outdoor lifetimes.The prior art also demonstrates soft mirror materials such as flexiblereflecting polymer films, polished metals, and acrylic refractors. Thesesoft materials were used for making curved solar reflectors becauseglass was considered hard, rigid, and brittle, and therefore would notbend sufficiently for nearby dish receivers. However, the soft materialsfailed in the field due to low efficiency, short-term lifetimes, poorspecular reflection, ultraviolet degradation, and excessive dirtbuildup. U.S. Pat. No. 4,372,772 describes a system bending flat glassmirrors in a solar dish concentrator which results in glass being bentto an extent previously thought not possible. However, this glass isonly bent and does not form parabolic curves, therefore does not formthe high-intensity uniform flux required by high-intensity photovoltaiccells.

[0006] There are three generic types of solar mirror concentrators;heliostats or central receiver type, parabola troughs or line focustype, and paraboloid dishes or point focus type. Heliostats aresubstantially flat reflectors concentrating sunlight onto distanttowers. The disadvantages of heliostats include critical mirror contourrequirements and the expense of tall towers supporting remote receivers.Troughs are simple-curve parabolic reflectors concentrating sunlightonto long receiver pipes spanning the full length of the reflectors. Thedisadvantages of troughs include low maximum solar concentration, highreceiver heat loss, and high receiver cost. Both heliostats and troughsdo not face directly at the sun therefore both have reduced performancesknown as cosine losses. Solar dishes are compound-curve paraboloidalreflectors concentrating sunlight onto small receivers supported nearthe centers of dish apertures. Dishes achieve the highest solarconcentrations, the best efficiencies, and face directly at the sun. Thedisadvantages of dishes includes the cost of compound and complexreflector curves and expensive mirror substrates. Both heliostats anddishes require accurate optical mirror contours and accurate opticaldual axis tracking. These optical accuracy requirements have beensignificant cost barriers in the prior art.

[0007] Prior-art solar dish concentrator methods and designs also havedisadvantages from unnecessary construction complexity. These includeforming compound and complex structural curves, molding substrates forcontrolling mirror curve contours, deflecting reflective membranes withair pressure, heat sagging glass for making fixed curved mirrors,structures with contiguous mirror support for mirror curve shaping,systems for avoiding mirror thermal stress from dissimilar structuralmaterials, curving mandrels, reflected laser light for mirroradjustments during construction, expensive motorized solar trackingdrives, tracking rails, and pivot bearings. Performance disadvantages ofthe prior art include shade from receiver supports and non-uniform fluxon high-intensity photovoltaic cells at the focus.

[0008] The advantages of the present invention resolves one or moreprior-art solar dish disadvantages with the simple use of readilyavailable materials manufactured in high volume from existing largeindustries. These materials are flexed into accurate parabolic curveswith existing skills and without special tools nor measurements. Curvedparts and curved templates are not used for construction. Substrates arenot used. Rather, spans of straight struts are parabolically curved andspans of flat glass mirrors are parabolically curved during constructionfrom deflection of rigid materials stressed with lateral forces. Thelateral forces are applied by a method of assembling the rigid materialsinto flexed solar dish concentrators. The stressed parabolic materialsdo not form permanent curves and would spring flat again ifdisassembled, thereby maintaining force reactions. This parabolicdeflection from force reactions demonstrates a natural phenomenon thatshows parabolic curves are formed from opposing forces, such as thecurves of wires between poles, the trajectory of canon balls, and thedeflection of horizontal structural beams from gravity. The disclosedinvention uses this phenomenon to make accurate parabolic curves fromflat raw materials flexed during assembly of solar dish concentrators inthe field.

[0009] All of the parts are the same size and are identical for easyassembly. This unity occurs when the mirror supporting framework isassembled perpendicular or normal to the dish aperture rather than, asthe prior art shows, assembled perpendicular or normal to the reflectingsurfaces. Trusses supporting paraboloid glass mirrors at specific anglesless than normal permit accurate parabolic trusses with equal focallengths to accurately support paraboloid glass with varying focallengths required by paraboloidal shapes and solar dish optics. The dishhas a rectangular aperture to support uniform rectangular glass for easyassembly and low waste manufacturing.

[0010] The flexed glass mirror solar dish concentrator is opticallyaccurate and delivers uniform high-intensity solar flux greater than1000 suns. Mirror shaping substrates are not necessary. Postconstruction adjustments are not necessary. The solar dish concentratorscan be constructed worldwide with indigenous skills and withoff-the-shelf materials at costs well below the current costs for fossilfuels. High volume solar dish manufacturing firms are not required forlow cost implementation. Special manufacturing tools are not required.

[0011] Thus, it is a general object of the present invention to providea paraboloidal glass mirror and a altazimuth solar tracking mirrorsupport framework which overcomes one or more of the disadvantages ofthe prior art noted above. Other objects and advantages will becomeapparent from the specifications and drawings.

[0012] It is a further object of the present invention to supply vastamounts of solar energy at costs substantially less than the costs offossil fuels, solar energy supplied from millions of light-weightdurable solar dishes assembled indigenously with heavy application ofavailable raw materials from large existing industries.

[0013] It is a further object of the present invention to provide aparaboloidal dish reflector apparatus which has a geometry particularlysuitable for quick assembly from identical parts without special toolsor skills.

[0014] It is a further object of the present invention to provide amethod for making accurate smooth paraboloidal space frames from flexedlinear members without curve measurements and adjustments.

[0015] It is a further object of the present invention to provide asystem and a method for flexing flat glass mirrors to form accurateparabolic curves without curve measurements and mirror alignments.

[0016] It is a further object of the present invention to provideaccurate glass mirror solar dishes made without mirror supportsubstrates.

[0017] It is a further object of the present invention to provideparabolic dishes suitable for reflecting uniform high-intensity solarflux onto concentrator photovoltaic cells.

[0018] It is a further object of the present invention to provide asystem for supporting dish receivers configured for minimum receivershading.

[0019] It is a further object of the present invention to provide asystem for accurately tracking solar concentrators towards the sun withoff-the-shelf weather resistant components mass produced for otherproducts.

SUMMARY OF THE INVENTION

[0020] Accordingly, the present invention is a parabolic solar dishwhich includes a rigid support matrix of substantially paraboloidconfiguration, which comprises a plurality of strut-like members whichare in turn joined together forming trusses substantially within planesparallel to the axis of symmetry of a paraboloid, planes that do notintersect the axis of symmetry of the paraboloid. The concave parabolicedges of the trusses are produced by patterns of intersections of theparaboloid and the aforementioned planes. This method of patterndefinition is used to create uniform trusses and uniform strut-likemembers throughout a paraboloid space frame. The method of connectingthe strut-like members flexes rigid linear truss rails into identicalsmooth parabolic curves.

[0021] The present invention also includes a system for flexingotherwise rigid flat glass mirrors which have a rectangular and slendershape. The system includes a space frame for supporting the slender flatglass mirrors near each mirror corner and button tension elementspositioned at predetermined points along the long edges of the slenderflat glass mirrors for applying forces normal to the reflectingsurfaces. The force flexes spans of the rigid slender flat glass mirrorsinto substantially accurate parabolic curves suitable for high-intensityuniform flux solar applications, such as illuminating high-intensityphotovoltaic cells. The mirror curve becomes hyperbolic near the mirrorcorners and sunlight reflected from this region will not be interceptedby high-intensity photovoltaic cells.

[0022] The present invention also includes a system for altazimuthtracking the angle of the sun. The system includes an azimuth drivesupport apparatus that adapts to not level ground for rotating the solardish concentrator utilizing a drive wheel, such as a bicycle wheel, incontact with the ground and a second wheel driving the rim of the drivewheel for speed reduction. A small gear motor drives the rim of thesecond wheel. A zenith tracking drive is made with a televisionsatellite dish actuator or screw-jack drive. Solar tracking becomesaccurate with small low-cost drive motors and solid statemicroprocessors. Reliability is enhanced with weather resistantcomponents such as bicycle wheels and dish actuators.

[0023] The present invention also includes a system for supporting asolar dish receiver at the apex of a cone of reflected sunlight. Thesystem includes two energy transport support tubes outside the cone ofreflected sunlight and two guy wires outside the cone of reflectedsunlight for supporting the receiver with minimum loss from direct shadeand reflected shade.

DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows an establishing view of a matrix solar dish.

[0025]FIG. 2 shows three parts used to make a paraboloidal space frame.

[0026]FIG. 3 shows a flexed parabolic truss.

[0027]FIG. 4 shows a sectional view of a matrix space frame.

[0028]FIG. 5 shows a close-up view of matrix space frame holes forvertical connectors.

[0029]FIG. 6 shows a row of identical rectangular slender flat glassmirrors.

[0030]FIG. 7 shows a method for making a parabolic glass mirrorreflector.

[0031]FIG. 8 shows a method for making a paraboloidal glass mirrorreflector.

[0032]FIG. 9 shows a row of parallel identical flexed parabolic trussesfor mirror support.

[0033]FIG. 10 shows a row of parallel identical flexed parabolic trussesfor frame support.

[0034]FIG. 11 shows a paraboloid matrix space frame.

[0035]FIG. 12 shows buttons flexing glass into parabolic curves.

[0036]FIG. 13 shows wires threading the buttons to an orthogonal mirrorsupport frame.

[0037]FIG. 14 shows a detailed view of the matrix dish.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0038] A preferred embodiment of the structure of the present inventionis illustrated in FIG. 1 (matrix solar dish) and FIG. 8 (stressedglass). These figures show parabolic flexing of long narrow strips ofglass mirror on a matrix of uniform flexed parabolic trusses. Thetrusses can be made identical if and only if they are defined by theintersection of a paraboloid and any plane parallel to the axis ofsymmetry of the paraboloid and not intersecting the axis of symmetry ofthe paraboloid. Trusses defined by such planes that contain the axis ofsymmetry are a special case forming the prior-art gore section dishesthat have a spider web appearance. This method of forming compoundcurves with identical off-axis trusses is exclusive and unique toparaboloidal compound curves.

[0039]FIG. 1 shows an altazimuth solar tracking system and a uniformflux high-intensity photovoltaic receiver located at a focal length of aparaboloid reflector. The focal length is defined as the distance fromthe center of a paraboloid reflector to the focus. Parabolic curvescontain focal lengths defined by the Cartesian coordinate formulaP=(X*X)/(4*Z) where P is the focal length of a simple curve. Thisformula creates the shape of solar trough or line focus reflectors.Paraboloidal curves are parabolic curves rotated around an axis ofsymmetry and the focal lengths are defined by the formulaP=(X*X+Y*Y)/(4*Z) where P is the focal length along the axis of symmetryof a compound curve. This formula creates the complex shape of a solardish or a paraboloid point focus reflector. The focal lengths of mirrorsnear the rim of a paraboloid dish are longer than the focal lengths ofmirrors near the center of the dish.

[0040]FIG. 2 shows three types of parts used to build a flexedparaboloid space frame. Identical copies of these three parts are usedthroughout the paraboloid space frame. Two truss rails 20 and 20 withzigzag webbing 22 and several optional identical vertical connectors 24are positioned as shown in FIG. 2 for assembly into a truss. There areother connection methods, such as rivets, that could eliminate thevertical connectors.

[0041]FIG. 3 shows truss rails 20 and 20 flexed into smooth paraboliccurves with lateral forces, and then connected to the zigzag webbingwith the vertical connectors to form a flexed parabolic truss 28.Lateral forces are applied by supporting the ends of the rails andpressing down on the along the sides of the rails. Smooth paraboliccurves are formed accurately from truss rail deflections caused byinternal truss rail stress reactions. The flexed truss rails do notyield and are not permanently bent, therefore would spring back flat ifreleased from the webbing. Any suitable webbing material may be attachedto restrain the flexed truss rails. Identically curved parabolic trussescould also be made by casting metal, by stamping sheet metal, by curverolling tubes, by forming composites, by assembling all straight shortstruts, or by other methods.

[0042]FIG. 4 is a sectional view of a paraboloidal matrix space frameshowing one of several ways that orthogonal flexed parabolic trusses mayshare common vertical strut connectors. The vertical connectors areparallel to the axis of symmetry of the paraboloid and normal to theaperture of the paraboloid. Therefore, the components of the flexedparabolic trusses may be uniformly separated along shared verticalstruts without changing uniform part dimensions or optics.

[0043]FIG. 5 shows one possible method of making connections with holes26 drilled through the truss rails and the vertices of the zigzagwebbing. The holes can be drilled accurately with a hand drill byinserting the truss rails into a pre-drilled steel pipe. The verticalconnectors are inserted through the truss rail holes and the zigzagwebbing holes then flared at both ends to form rivet heads. The shanksof the vertical connectors would have burrs or stops or additionalconcentric shorter tubes to sandwich the zigzag webbing against thetruss rails. An alternative connection would insert rivets through theholes then expand the rivets inside the ends of the vertical connectorsforming pregnant vertical connectors. There are other methods forconnecting truss members together such as spot welding or usingbrackets.

[0044]FIG. 6 shows a row of identical unsupported rectangular slenderflat glass mirrors 30 made from silver laminated to low-iron float glassof uniform thickness. The number of flat glass mirrors used isdetermined by receiver flux intensity requirements. Other types of flatglasses and flat mirror laminates could be used for making flatglass-like specular solar dish mirrors.

[0045]FIG. 7 shows a method of flexing a row of slender flat glassmirrors into parabolic curves with a row of identical straight trusses.A row of parabolic glass mirrors 32 is formed by supporting the shortsides of rectangular slender flat glass mirrors 30 on two orthogonalstraight trusses 34 and 34 then allowing the glass mirrors to sag fromthe force of gravity. Additional orthogonal straight trusses 36 arepositioned under the parabolic glass mirrors for applying flexing forcesto the glass when the glass is tilted out of plane with gravity and forsupporting the glass under blizzard and hurricane loads. Tension buttonsor other systems are used between the parabolic glass mirror edges andtruss rails at the locations where straight trusses 36 crossorthogonally the parabolic glass mirror edges. This action of flexingthe flat glass mirrors down toward the orthogonal trusses causes flatglass mirror spans between the trusses to deflect into accurateparabolic curves. The glass force reactions from the flexing forcesoccur on trusses 34 and 34 thereby restraining the mirrors in place.There are other configurations and tension materials that can also beused to flex slender flat glass mirrors into accurate parabolic curves.FIG. 7 illustrates a line focus or parabolic trough solar concentrator.The focal lengths of all the mirrors are identical.

[0046]FIG. 8 shows the method of flexing flat glass mirrors into asubstantially paraboloidal dish curve with identical flexed parabolictrusses. A paraboloidal array of glass mirrors 38 is formed bysupporting rectangular slender flat glass mirrors 30 near the mirrorcorners on two orthogonal flexed parabolic trusses 28 and 28 thenallowing the glass mirrors to sag from the force of gravity or by otherforces. Additional flexed parabolic trusses, all identical to flexedparabolic truss 28, are positioned under the paraboloidal array of glassmirrors for applying flexing forces to the glass when the glass istilted out of plane with gravity and for supporting the glass underheavy weather. Tension elements are used between the glass mirrors andorthogonal truss rails. A glass force reaction from the flexing forceoccurs between the glass corners and the flexed parabolic trussesthereby holding the mirrors in place. There are other configurationsthat can also be used to flex slender flat glass mirrors into parabolicand hyperbolic curves with space frames. FIG. 8 illustrates a pointfocus or parabolic dish solar concentrator. The focal lengths of theparabolic mirrors change with mirror location on the dish. The mirrorsnear the center have shorter focal lengths than the mirrors near theedges.

[0047]FIG. 9 shows a mirror support frame 40 comprised of a row ofparallel identical flexed parabolic trusses. The actual number oftrusses used is determined by the ability of spans of unsupportedstressed glass mirrors to withstand maximum wind, snow, and ice loads.

[0048]FIG. 10 shows a truss support frame 42 comprised of another row ofparallel identical flexed parabolic trusses. Truss support frame 42 isidentical to mirror support frame 40.

[0049]FIG. 11 shows a paraboloidal matrix space frame 44 formed from themirror support frame and truss support frame arrayed orthogonally andconnected together with common vertical connectors 24 as shown in FIG. 4and FIG. 5. The entire paraboloidal matrix space frame is flexed fromthree identical-sized components; truss rails 20, zigzag webbing 22, andvertical connectors 24. Mirror support frame 40 within paraboloidalmatrix space frame 44 is used to flex mirrors as shown in FIG. 8. Thereare other methods for supporting mirror support frames 40 such as torquetubes (not shown) connecting a row of identical flexed parabolic trusses28 held in a paraboloidal shape.

[0050]FIG. 12 and FIG. 13 show a row of slender flat glass mirrors 30curved with a tension elements or buttons 46. The glass mirrors shouldbe thick enough to withstand heavy wind, snow, and ice between tensionelements, and thin enough to flex into parabolic curves suitable forsolar dish optics. The glass mirrors should be long enough to minimizethe effect of fixed hyperbolic curve errors located near the glassmirror comers. Rectangular slender flat glass mirrors 30 are shownpositioned over orthogonal flexed parabolic trusses 28. The glassmirrors are supported near the corners and then flexed into paraboliccurves with forces normal to the reflecting surfaces. Curves are notused during construction. Parabolic glass curves are created duringconstruction from deflection of rigid flat glass resisting lateralforce. The glass mirrors are not permanently curved and would springback flat again if released from the support frame. Buttons 46 or othersystems are used to maintain tension between the glass mirrors and theorthogonal trusses. Wires 48 are used as button thread to connect thebuttons to the orthogonal trusses and sandwich consecutive glass mirroredges against the orthogonal truss rails. The wires makes flexibleconnections between the glass mirrors and the truss rails therebyallowing for thermal expansion stress. The glass mirrors make loosecontact with the orthogonal truss rails at points under the buttons. Theglass mirrors are firmly held in place by the glass corners pressinghard against the outside trusses. This pressing force is a reaction fromflexing stress, a force approximately equal to mirror weight. Othertension mechanisms connected to alternate support frames could also beused for flexing slender flat glass mirrors into parabolic curves.

EXAMPLE

[0051] For example, a solar dish is made with fifteen rectangles oflow-iron window glass 3300 millimeters long, 230 millimeters wide, and 2millimeters thick. The glass is coated with silver protected by copperdepositions and paint layers. The mirrored glass is then forced towardsan orthogonal support frame every 470 millimeters excluding the ends,thereby flexing and stressing the rigid glass mirror causing the glassmirror to deflect and form continuous accurate parabolic curves withfocal lengths commensurate with a dish containing a 3300 millimeterfocal length. Hyperbolic mirror surface errors in this example would bewithin 125 millimeters from the ends or corners of the glass mirrors,less than 8% of total mirror area. The hyperbolic curve area is fixedand independent of mirror length. Only long glass mirrors can besubstantially deflected into parabolic curves without contiguouscurve-forming substrates. In this example, a 1000 sun high-intensityphotovoltaic receiver would be 40 millimeters wide and 250 millimeterslong with a wider heat exchanger to transfer surface heat to fluids, andto collect the 8% sunlight reflected from the hyperbolic mirror curveslocated near the mirror corners.

[0052]FIG. 14 shows an altazimuth support carriage supporting a matrixsolar dish concentrator with a rectangular aperture 88. A hollowconcrete column 50 with an embedded polymer tube 52 supports a tee-bar54. The tee bar rotates freely in the azimuth direction on centering pin56. A square frame 58 is connected to the tee-bar at two zenith bearings60 and 60 which could be just dry pins through drilled holes in thesquare frame. This square frame moves freely in the zenith direction. Anazimuth drive support 62 is connected to the tee-bar at zenith bearings60 and 60 and moves freely in the zenith direction to accommodate notlevel ground. An azimuth ground wheel 64, such as a bicycle wheel, isconnected to the azimuth drive support and rolls along the groundleaving a trail or path 66. An optional second wheel 68 drives theground wheel rim with a friction hub 70 for speed reduction. A smallazimuth gear motor 72 is attached to the azimuth drive support anddrives the wheel assembly rim with friction to track the matrix dishglass reflector in the solar azimuth direction. A zenith screw jackdrive motor 74, preferably a low-cost television satellite dishactuator, is attached between the tee-bar and the square frame to trackthe matrix dish glass reflector in the solar zenith direction. Tworeceiver support tubes 76 and 76 are attached to the square frame andare used to carry fluids, power, and hydrogen from a receiver 78. Thereceiver is designed with abundant fluid surface area for heat removalvia a bundle of tubes or extensive channels. The receiver support tubesare connected together at an apex 80 above a cone of reflected sunlightfocused on receiver 78 and held in place with two receiver guy wires 82and 82 connected at apex 80. Active or passive heat shields (not shown)are used near the receiver to protect this low-shade receiver supportstructure from off-sun scorching. A shadow-band solar eye box 84 isattached to a receiver support tube and houses four light detectorsbeneath two spherical lens and a microprocessor for active and passivesolar tracking and to control receiver functions. Razor sharpshadow-band dividers, such as razor blades, are positioned at the focuspoints of the spherical lens and the light detectors are located on bothsides of both dividers well below the lens focal planes and connected tothe microprocessor thereby making digital active solar tracking veryaccurate. Two counterweights 86 are attached to the square frame tobalance the dish and to reduce mechanical and electrical loads on thezenith drive. The matrix solar dish is attached to the square frame withfasteners between the square frame and some of the vertical strutconnectors. A hail hood (not shown) could be attached to the leadingedge for heavy hail protection.

[0053] In operation, a small amount of electrical power is applied tothe microprocessor and to the azimuth and zenith drive motors. Water orother cooling fluids are pumped through the receiver support tubes andthrough the receiver. The microprocessor attempts to look at the sun andchecks the time and dish position and system diagnostics then signalsthe azimuth and zenith drive motors to position the matrix solar dishnormal to the sun. The azimuth gear motor drives the speed reducer wheeland ground wheel to rotate the tee-bar in the hollow column. The zenithdrive motor tilts the square frame relative the tee-bar. Upon facing thesun, irradiating up to 850 Watts per square meter, the microprocessorrecords the time, date, and dish position into permanent memory forfuture reference for solar tracking during cloudy weather with passivetracking routines. The parabolic mirrors on the paraboloid surfacereflect uniform high-intensity sunlight onto the receiver. The receivergenerates hot water or other hot fluids from black heat exchangers atbetter than 90% efficiency and generates electricity from high-intensityphotovoltaic cells at better than 30% efficiency and could manufacturehydrogen and oxygen from electrolysis of water. The receiver can alsodrive other chemical reactions and physical devices. The hydrogen isrecycled in a fuel cell to reproduce electrical power and water when thesun is not available. The hot water is used locally or powers a districtheating system.

[0054] During snow storms and heavy hail conditions the microprocessoron the dish frame would signal the zenith drive motor to face the dishmirror aperture towards the horizon for protection of the glass mirror.

[0055] While a simple light-weight durable solar dish is preferred, lessthan 15 kilograms per square meter, many other variations of the solardish could also be deployed such as utilizing multiple quadrants ofmirror arrays or other mirror configurations such as off-axis paraboloidfocus locations. The dish could alternately be assembled with supportedglass mirrors, curved mirrors, or reflectors not made from glass. Mirrorsupports can be assembled onto frames which are not paraboloidal, orframes which are not formed from curved or flexed trusses. Mirrortension elements can be a wide variety of devices spanning either sideof flexed mirrors such as compression orthogonal strips across thewidths of the concave sides. Alternate solar tracking systems can alsobe used such as polar mounts and tripod mounts. Alternate receiversupport systems can also be used with this solar dish includingstationary receiver supports. Accordingly, the scope of the inventionshould not be determined by the embodiment illustrated, but by theappended claims and their legal equivalents.

What is claimed is:
 1. A method for making a paraboloid space frame fordirectly supporting rectangular mirrors on a solar dish concentrator,said paraboloid space frame containing parabolic trusses withsubstantially identical focal lengths, said method comprising the stepsof: a. providing a plurality of parabolic trusses, said parabolictrusses containing identical focal lengths; b. positioning saidparabolic trusses substantially within planes that do not intersect theaxis of symmetry of a paraboloid shape; c. positioning said parabolictrusses such that the concave edges of said parabolic trusses liesubstantially on the concave surface of said paraboloid shape; d.connecting said parabolic trusses to a support frame; whereby a solardish space frame will be assembled from identical parts forming an arrayof identical parabolic trusses containing identical focal lengths fordirectly supporting an array of parabolic mirrors containing separateand unequal focal lengths as required by paraboloidal dish geometry. 2.A method of claim 1 , wherein providing said parabolic trusses byforming curved parabolic trusses, said method comprising the steps of:a. providing slender truss rails with rigid connecting members; b.restraining the ends of said slender truss rails; c. forcing saidslender truss rails with lateral force; d. allowing spans of saidslender truss rails to deflect into substantially parabolic curves; e.attaching said rigid connecting members between the parabolically curvedslender truss rails; whereby said slender truss rails with said rigidconnecting members will become flexed parabolic trusses defining smoothparabolic curves with identical focal lengths.
 3. A method of claim 1 ,wherein providing said support frame by providing a row of saidparabolic trusses forming an orthogonal matrix of parabolic trusses,said method comprising the steps of: a. positioning a first row ofidentical parallel parabolic trusses for mirror support; b. positioninga second row of identical parallel parabolic trusses forming saidsupport frame orthogonal to said first row of identical parallelparabolic trusses; c. connecting the first row of parabolic trusses andthe second row of parabolic trusses together forming a paraboloidalspace frame matrix of orthogonal parabolic trusses; whereby aparaboloidal solar dish space frame will be assembled from identicalparts.
 4. A method for making rectangular parabolic glass mirrors foruse in solar dish concentrators, said method comprising the steps of: a.assembling a mirror support space frame; b. providing rectangularslender flat glass mirrors which are shaped substantially long andnarrow with uniform thickness; c. positioning said slender flat glassmirrors directly over said mirror support space frame; d. supportingcorner areas of said slender flat glass mirrors directly on said mirrorsupport space frame; e. forcing said slender flat glass mirrors towardsaid mirror support space frame; f. allowing spans of said slender flatglass mirrors to deflect forming substantially parabolic curves withvarious focal lengths; whereby said slender flat glass mirrors will beflexed forming various parabolic curves containing various dish mirrorfocal lengths, parabolic curved glass mirrors formed without reflectorcurve-forming substrates, and supported directly on a solar dish frameat said corner areas from glass flex force reactions.
 5. A method ofclaim 4 , wherein a force of forcing glass mirrors is applied byproviding a plurality of tension elements positioned at predeterminedpoints along the long edges of said slender flat glass mirrors and byconnecting said tension elements to said mirror support space frame,thereby providing points of force substantially normal to the reflectingsurfaces of said slender flat glass mirrors urging unsupported spans ofsaid slender flat glass mirrors to deflect into substantially paraboliccurves.
 6. A method of claim 4 , wherein assembling said mirror supportspace frame by assembling a rectangular paraboloid space frame fromcurved parabolic trusses containing identical focal lengths, saidparabolic trusses assembled from identical parts, said method comprisingthe steps of: a. providing identical slender truss rails with identicalrigid connecting members; b. restraining the ends of said slender trussrails; c. forcing said slender truss rails with lateral force; d.allowing spans of said slender truss rails to deflect into substantiallyidentical parabolic curves; e. attaching said rigid connecting membersbetween flexed slender truss rails forming identical parabolic trussescontaining identical focal lengths; f. positioning said parabolictrusses parallel in a rectangular array over said support frame; g.fastening said parabolic trusses onto said support frame; wherebyparabolic glass mirrors flexed to different focal lengths will bedirectly supported on a paraboloid space frame assembled from parabolictrusses flexed to identical focal lengths, resulting in a paraboloidalsolar dish made from identical parts.
 7. A paraboloid frame forsupporting mirrors in a solar dish concentrator, said paraboloid framecomprising uniform components, said paraboloid frame further comprising:a. a plurality of parabolic trusses, said parabolic trusses havingidentical focal lengths; b. a truss support frame; c. means forpositioning said parabolic trusses on said truss support frame forming aparaboloid shape containing a rectangular aperture; d. means forattaching said parabolic trusses to said support frame;
 8. A paraboloidframe of claim 7 , wherein means for connecting a parallel row of saidparabolic trusses orthogonally with another parallel row of saidparabolic trusses to form an orthogonal matrix of said parabolictrusses, whereby said paraboloid frame will be assembled with orthogonalparabolic trusses containing identical focal lengths, said paraboloidframe containing a rectangular aperture.
 9. A system for makingrectangular parabolic glass mirrors for use in solar dish concentrators,said system further comprising: a. a plurality of rectangular slenderflat glass mirrors which are shaped substantially long and narrow withuniform thickness; b. a mirror support frame; c. a plurality of mirrortension elements; d. means for supporting corner areas of said slenderflat glass mirrors directly on said mirror support frame with saidmirror tension elements; e. means for forcing said slender flat glassmirrors toward said mirror support frame with said mirror tensionelements; whereby said slender flat glass mirrors will be flexed intoaccurate parabolic curves without contiguous mirror support substrates.10. A system of claim 9 , wherein said mirror support frame comprising:a. a plurality of curved parabolic trusses containing substantiallyidentical focal lengths; b. a truss support frame; c. means forpositioning said curved parabolic trusses on said truss support frameforming a paraboloid shape containing a rectangular aperture; d. meansfor attaching said curved parabolic trusses to said support frame;whereby parabolic glass mirrors flexed to different focal lengths willbe directly supported on a paraboloid space frame assembled fromparabolic trusses flexed to identical focal lengths, resulting in aparaboloid solar dish made from identical parts.
 11. A solar dishconcentrator, comprising: a. a truss support frame supported on analtazimuth tracking system; b. a system supporting a receiver near thefocus of said solar dish concentrator; c. a plurality of rectangularslender flat glass mirrors which are shaped substantially long andnarrow with uniform thickness; d. a plurality of parabolic trussescontaining substantially identical focal lengths; e. means forpositioning and attaching said parabolic trusses onto said truss supportframe; f. means for flexing said slender flat glass mirrors directlyagainst said parabolic trusses; whereby a tracking solar dish with areceiver support is provided with glass mirrors accurately curved tovarious focal lengths, glass mirrors flexed by parabolic trussescontaining identical focal lengths.
 12. The solar dish of claim 11 ,wherein said altazimuth tracking system has an azimuth drive systemcomprising: a. means to support a solar dish on a spindle that canrotate in the azimuth direction; b. means for supporting an azimuthdrive apparatus with bearings to follow not level ground; c. means forrotating the solar dish concentrator with a gear motor coupled to adrive wheel in contact with the ground.
 13. A system of claim 12 ,wherein means for providing azimuth speed reduction using a second wheelcoupled to said drive wheel, whereby solar tracking becomes accuratewith a small drive motor.
 14. The solar dish of claim 12 , wherein saidaltazimuth tracking system has a zenith drive system comprising ascrew-jack motor, zenith bearings, and means for tracking the sun with amicroprocessor and a spherical lens.
 15. The solar dish of claim 11 ,wherein the system supporting a receiver near the focus comprising ameans connecting two tubes and two guy wires forming a receiver supportstructure positioned beyond an apex of a cone of reflected concentratedsunlight, whereby the receiver is blocked by minimum direct shade andminimum reflected sunlight shade.
 16. The solar dish of claim 11 ,wherein said parabolic trusses comprising identical truss rails,identical rigid truss webbing, and means for connecting the truss railsand truss webbing together forming identical curved parabolic trussescontaining substantially identical focal lengths.